1. Field of the Invention
The invention is related to the field of flow meters, and in particular, to Coriolis flow meters.
2. Description of the Prior Art
Because Coriolis Flow meters don't have any internal moving parts there is nothing to wear or break. Therefore in a clean fluid, the expectation is that the flow meter will not change its measurement characteristics over time. Unfortunately some fluids may cause corrosion or erosion of the conduits inside the flow meter. Another problem may occur for fluids that can deposit coatings along the internal diameter of the conduits in the Coriolis flow meter. Both types of activities (removing material or depositing material) may cause the flow meter measurement characteristics to change. One way to detect and correct these problems is to prove the flow meter to recalibrate the meter's measurement characteristics. Proving is a field calibration method where a known volume is flowed through the flow meter and compared to the flow measured by the flow meter. Provers can be stationary, e.g. mounted permanently next to the meter, or truck mounted so that the prover can calibrate a plurality of meters. A typical prover is a device with a pipe (104) of a known internal diameter. A ball or piston (102) slides inside the pipe (104) and passes two sensors (S1,S2) or detectors. The first sensor (S1) signals the prover's computer to start counting pulses from the flow meter being calibrated. The pulses are typically proportional to volume flow rate. The second sensor (S2) signals the prover to stop counting pulses from the meter being calibrated. The volume inside the pipe between the two detectors is well known and often compensated for pressure and temperature. The total volume between the two detectors is compared to the number of pulses from the flow meter and a meter factor is determined. The meter factor is simply a correction factor applied to the meter's output. Depending on the volume of the prover and the flow rate used, the measurement time for the known volume to pass through the flow meter may be from 0.5 seconds to 60 seconds. Provers often have a length of pipe that the ball or piston travels before crossing the first detector. This length of pipe is typically called the “prerun.” The prerun length is equivalent to a fixed volume. The prerun time is dependent on flow rate. At high flow rates, the prerun time may be quite short.
Another way that the meter's measurement characteristics can be verified is by measuring the density of a material having a well known density. When the density measurement from the flow meter matches the known density, the meter's measurement characteristics are still accurate. See for example U.S. Pat. No. 6,092,409 “System for validating calibration of a Coriolis flowmeter” issued Jul. 25, 2000, which is hereby incorporated by reference for all that it teaches. Unfortunately, verifying the meter's measurement characteristics by measuring density or by proving, requires an operator that is familiar with the operation and settings of the Coriolis flow meter. Obtaining an experienced operator to verify a meter's measurement characteristics is not always possible.
Therefore there is a need for a system and method for guiding a user through the steps for using the meter to complete a predefined task.